Tire cord fabric is one of the main reinforcement material used in tire. Since the rubber cannot provide the sufficient force to meet all forces generated by the tire-road interaction, tire cord fabric is used to reinforce the mechanical features of the rubber. In tire cord fabric, twisted yarn and weft materials are used in weaving tire cords in order to acquire unidirectional cord fabric structure.
There are three main processes in tire cord fabric production.
The first one is twisting. Filament yarns (such as polyamid 6, polyamid 6.6, polyester, aramide, PEN, carbon fiber, rayon, fiber glass) are twisted as 50 to 800 tpm. Then, in order to provide tire cords as cable, the said twisted yarns are twisted either in opposite direction (SZ or ZS twist directions) or in same direction (SS or ZZ twist directions) together. The twist level depends on the material, the linear density of the yarn and the technical feature that is desired for the final product. Normally, the tire cords are twisted in S (or Z) and Z (or S) directions, and twisting process is performed in twisting machines.
The second process is called as weaving. This process comprises combining the twisted cords in order to create a fabric with twisted cords. It is performed in weaving machine by using weaving loom. There are two main components in weaving. These are twisted cords called as warp and weft. Warp is the main component of the tire cord fabric, and the weft cords are the support components which enable to form a whole by passing between the warp cords which are the main component. The loom is used for performing weaving process, and enables to pass the wefts between the parallel placed warps such that they will have 90 degree angle with the warps in order to form fabric structure. The number of the wefts in 10 centimeters is referred as PPD, and the number of warps in 10 centimeters is referred as EPDM. In general, EPDM level is much bigger in an ordinary fabric than the PPD level.
Mostly, this ratio (EPDM/PPD) is minimum 8 and it can be up to 12. The fabric manufactured in weaving machines is called as greige fabric.
Finishing is the third and last process in tire cord fabric production. Finishing process is performed in finishing unit. The fabric is coated with a proper adhesive which enables the connection between the cord and the rubber. Then the cords are dried and hot stretched at a certain temperature in order to provide the desired physical features. The final product is called as finished fabric.
As a result of these processes (twisting, weaving and finishing), defected products lack of technical features can be formed such as missing cord, filament cord, gap and fabric margin, folding, the cord getting loose from the fabric, and the fabric width being more or less than determined or weft density in all these cases, even if the fabric is ready to send to the customer, these problems should be eliminated. If these defects are not eliminated, the fabric may become scrap or can be sold as second class fabric.
In order to take care of the defect or some quality problems, the warp and the weft should be separated in order to cut the fabric and make the correction. That is, it should be woven again as it is required by the features of the fabric. This re-weaving process is performed with a unit called as “re-weaving machine”.
In the state of the art, re-weaving is performed by passing the stages of let-off stand, pull roll, cutters, rotator blade, weaving loom, wind-up stand. Re-weaving applications start by taking the defected fabric roll to the let-off stand. The let-off stand which is the first stage of re-weaving process enables the fabric to be aligned properly in the inlet of the system. The fabric will progress on the pull rolls. Generally there are two rolls in each set of pull rolls. The fabric is drawn with tension from the let-off stand depending on the speed of the weaving machine generating reactive force based on fabric weight. Then the fabric moves to the cutter. A set of cutter usually has 50-60 blades, and each cutter an opening with about 30 mm2 fixed with cutter holding rod. These cutters cuts weft yarn with about 20-30 cords/group depending on the fabric width, dtex level and weft density. Aside from these limits, the re-weaving machine cannot cut the wefts properly, and this causes the cords to break during process. Especially, when the weft density is above 6 PPD, cutting cannot be performed properly and the wefts cannot be collected with rotator blades.
Then the fabric is passed from the rotator. The rotator separates each cord of the fabric in opposite directions, and it is rotated by the electric engine in order to separate the remaining weft. During the rotational movement which the rotator makes, it creates vibrations to separate the weft remaining on the warp. In this stage, the cutter can cut the warp due to the rotational movement of the rotator which enables the warp cord to move upwards and downwards. If some cords contact the blade, they can get damages and break. Since only a set of cutting blades are used, cutting should be completed in single step; this may cause damage and thus loss in breaking strength. In case the finished fabric is re-woven, the current system cannot operate to remove the finished weft yarn properly, because the weft yarns are adhered to the wefts because of the adhesive coating in finishing process.
After the wefts are cut and collected in the rotator blade, the warps of the fabric are guided to the re-weaving machine for being woven again. This step provides a solution by restructuring the defected part of the fabric by starting over. The weaving machines used in this process can have a pleating machine which performs the weft rotation mechanically or any pleating machine that can operate at maximum speed which is approximately at 250 m/mn. Cutting and weft collection cannot be performed properly at higher re-weaving speeds. The final stage of the re-weaving process is to winding the rewoven fabric. All required parameters are controlled and confirmed at this step.
The re-weaving machine in current applications with the techniques known in the state of the art has four main deficits. The reweaving machines can operate in linear densities changing between 900 to 1700 dtex. Since the cord fabric has higher linear density than 1700 dtex in tire industry, the said fabrics cannot be rewoven properly. Second, in the current applications, the fabrics having weft density more than 8 PDD cannot be rewoven. The higher the pick density is, the more difficult to take the wefts from the processed fabric is. Thirdly, the weft material should be cotton or polyrayon or cotton with very low elongation. If the weft material has an elongation higher than 10/breaking value, the reweaving machine cannot cut the wefts, therefore the wefts cannot be cleaned from the fabric. Finally, the maximum machine speed can be 250 meters in a minute. Otherwise, weft cutting and cleaning cannot be performed. Since these limits cannot be overcome, reweaving machine cannot take the wefts from the fabric and reweaving process cannot be performed properly.
In addition to the technical capacity of the reweaving machine, the breaking strength of the fabrics rewoven with the current applications significantly drops because of the high and unstable friction during weft cutting process. This generally causes unwanted fabric features and causes too much scrap because of the cord breaking during process.
Due to the tight limitations in the current machine adjustment, reweaving cannot be performed for tire cord fabrics in all kinds properly. Especially, if the linear density of the warp is higher than 1700 dtex, reweaving cannot be performed. If the weft density is higher than 6 PPD, many problems such as the loss of breaking strength and the cords breaking during the process can be seen. Reweaving cannot be performed in weft densities higher than 8 PPD. Additionally, if the weft material has elongation at break value higher than 10%, the cutters cannot cut and thus reweaving cannot be performed properly. In case the current application is performed, the process speed of the reweaving cannot exceed 250 meters per minute.
In the previous art, since the cutters are placed after the pull roll, the tension of the warps cannot be kept stable, and causes the wefts to be cut improperly since there is no possibility to adjust the cutting blades in the holding rod.
Canadian Patent Document No CA257823 is known in the state of the prior art.